Christopher Plummer delivers a particularly charming performance in this entertaining film set during wartime. The story follows "Eddie Chapman," a small-time burglar who finds himself embroiled in the German occupation of Jersey. At first doubtful, the local commander recognizes that this confident young man could be valuable – and he seems eager to help, provided the compensation is sufficient. He’s subsequently dispatched to England, where he immediately contacts British authorities, offering his services while explaining that the Germans think he's their operative. Soon after, he returns to Germany under the guidance of "Baron von Grunen" (Yul Brynner) and Gert Fröbe ("Col. Steinhager"), planning further acts of sabotage – and ensuring a generous profit for himself along the way. The narrative is inspired by a true story, although I suspect Plummer has added some humor and a sense of national pride to the character that may not have been present originally. The three actors share good chemistry, and there's a fair amount of amusing suspense as "Chapman" becomes involved with the alluring resistance fighter "Paulette" (Claudine Auger) and "Countess Helga" (Romy Schneider), both of which threaten his safety and the success of his delicate mission. Sadly, it feels excessively lengthy; while the plot is good, Terence Young has difficulty maintaining audience engagement for over two and a quarter hours. Nevertheless, the ending proves satisfactory.

Source on TMDB